1. Field of the Invention
The present invention generally relates to the supply of remotely controlled electronic components and especially, but not exclusively, to non-contact smart cards, that is to say cards communicating remotely with a terminal, and for which the transmission of the data on the card to the terminal is conventionally done by absorption modulation. One particular application of the invention relates to non-contact smart cards called xe2x80x9cclose couplingxe2x80x9d smart cards which may also be introduced into a reader.
Non-contact smart cards are also supplied via the same channel as that used for the data transmission. In practice, the chip on the card includes an inductive interface, such as a coil, interacting with a coil of the remote terminal. The decoding of the data transmitted from the card by absorption modulation includes measuring, at the coil of the terminal, the voltage variations corresponding to the data transmitted and generated by the modulation means of the chip.
2. Description of the Relevant Art
At the present time, the number of integrated functions on the same electronic chip is constantly changing. Increasing the number of functions means increasing the number of transistors used and significantly increasing the amount of power consumed. As a result therefore, during operation of the electronic components of the chip, there are large variations in current consumed or absorbed. These variations in the current consumed induce currents in the coil of the chip which are mixed with the actual modulation current. The voltage variations obtained at the coil of the terminal then comprise not only the voltage variations generated by the absorption modulation but also these xe2x80x9cspuriousxe2x80x9d voltage variations caused by the variations in the consumption of the electronic components of the chip. The decoding of the information transmitted is then disturbed and the data transmission may even, in the worst possible case, be interrupted.
In one embodiment a card is configured to prevent the variations in current absorbed by the electronic components of the chip from disturbing the data transmission and to obtain reliable data transmission whatever the variations in the current consumed by the remotely powered integrated circuits.
In one embodiment, a stabilized power supply device for an assembly of remotely powered electronic components, for which the supply and the data transmission take place on the same channel via an inductive interface such as a coil is provided. The device includes an electronic module which, interposed between the inductive interface and the assembly of electronic components, supplies the assembly of electronic components with a variable current, that is to say one which may vary depending on the variations in consumption by the electronic components, so as to ensure that the proper operation of these electronic components is satisfied, and consumes a constant current, so as to allow effective data transmission.
According to one embodiment, the electronic module includes a current generator delivering a constant current and a constant-voltage shunting means (or shunt) (for example, an n-MOS transistor biased by a resistance bridge) connected in parallel with the assembly of electronic components.
Advantageously, the constant current delivered by the current generator is at least equal to the maximum current consumed by the assembly of electronic components.
The constant current generator may be controlled by a reference circuit by means of a constant voltage.
Preferably, the electronic module includes two filtering capacitors so as to remove the high-frequency signals.
The interface includes a coil connected to a full-wave rectifier, the coil being the seat of a voltage induced by the magnitude field of a remote inductor (for example, the coil of the terminal communicating with the smart card).